LONDON—A U.K. investigation into potential manipulation of currency markets is looking at a former trader at Royal Bank of Scotland Group PLC who participated in electronic chat sessions with traders at other banks, according to people familiar with the investigation.

Richard Usher, currently J.P. Morgan Chase & Co.'s London-based head of spot trading for Group of 10 currencies in the region covering Europe, the Middle East and Africa, took part in the chat sessions with top traders from various financial institutions...